This invention relates generally to a snug fitting apparatus for a tire assembly having a tire fitted to a disk wheel for use in automobiles and the like and, more particularly to an apparatus for making the fit between the tire and the disk wheel rim tight.
The tire assembly made by fitting the tire to the disk wheel and being filled with air exhibits slight unbalance in mass distribution due to variation in the tire dimensions, rigidity, weight distribution, true circle accuracy of the disk wheel, and the state of fit between both of the components, which causes vibration and adversely affects riding comfort and maneuverability when a vehicle is driven. Therefore, various measures are taken to solve the problem of the unbalance.
Here, the state of fit between the tire and wheel is settled when air is injected to inflate the tire to a specified shape at the time of assembling the tire.
However, in some cases the air injection only is not sufficient to produce a snug and stabilized state of fit, and unbalance may result. Therefore, a process of correcting the incomplete fit between tire and rim is employed in which a lateral force that can occur during actual vehicle run is applied in advance to the tire assembly to make the fit between tire and rim snug.
As a means for applying the lateral force to the tire assembly, one is proposed (Japanese patent publication No. Sho-64-3683) in which a large diameter drum of normal-and-reverse rotation type with a slip angle is pressed against the ground contact surface of the tire and rotated. The main point of the work of fitting together the wheel and tire is to bring about a normally fit state of the tire assembly with the dummy load before the tire assembly is brought to a stabilized state with the actual load. However, it is generally known through experience that what is practically necessary is not the fit state according to the design theory but a stabilized fit state brought about with the actual load of the vehicle. However, curvature of the roller of the prior art for applying the lateral force is very sharp in comparison with the flatness of the road surface. As a result, the load is not distributed evenly, the pressing force is dispersed around the tire contact area, and the pressing force to the fitting surface is very different from that with the actual vehicle. Moreover, the stresses in the tire is constantly similar to those produced when the tire negotiates a projection on the ground. This sometimes results in that the pressing force does not act on the wheel-tire fit interface.
Another problem with the prior art is a necessity of a device to give swinging motions to the tire so that the lateral force is applied to one and the opposite sides of the tire by turns, which increases the overall size of the correction apparatus.
Therefore, an apparatus has been proposed in a Japanese utility model publication No. 2553192 that is compact, simple, and effective to simulate the actual load very closely by making the pressing surface for applying the lateral force very similar to the ground surface on which the actual vehicle runs. The apparatus is constituted to perform a snug fitting process by pressing the ground contact area of the rotating tire assembly to apply a lateral force to that area. The apparatus comprises a plurality of rollers arranged side by side close to each other with a slip angle to form a set (or a group) of pressing rollers. The rollers as a single set (or a single group) are pressed against the ground contact surface of the tire assembly.
With the above constitution, since the group of pressing rollers is constituted with the plurality of rollers arranged side by side close to each other, a wide pressing surface is formed which is similar to the ground surface on which the actual vehicle runs, and the similar load to that in actual situation acts on the ground contact surface of the tire assembly. Another advantage is that since gaps of a certain size are produced among the rollers, the pressing surface becomes irregular to some extent and is very similar to the irregular road surface, and similar loads to that occurring when the actual vehicle runs act on the tire assembly.
As described above, the snug fitting process apparatus has been proposed with which the ground contact surface moving along its entire circumference of the tire assembly is pressed to improve the snugly fit state between the wheel and tire so that the vibration due to non-uniform fit state between the rim and tire is prevented from occurring. However, since such a process is applied under constant conditions on production lines, the effect of the snug fitting process must be checked appropriately.
The checking work is conventionally made as follows: Samples are taken at specified quantity intervals of the products and the uniformity in the fit state is checked with a uniformity checking machine to determine acceptability of the degree of uniformity. However, such a checking method has the following problems.
First, the uniformity checking machine presses a drum of an outside diameter as large as about 850 mm against the ground contact surface of the tire assembly and measures the magnitude of variation in the radial force (RFV), the magnitude of variation in the lateral force (LFV), and the magnitude of the force in the tangential direction (TFV) of the tire, and the machine is large-sized and expensive. From another aspect, the most important factor in the snug fitting process is the magnitude of the RFV on which the riding comfort and maneuverability largely depend. Therefore, although the uniformity checking machine detects variations in various forces with high accuracy, the measurements can be said superfluous and too much time is taken to obtain the results.
Second, since the check is performed by sampling, the processed state cannot be assured for all the products and the quality is assured only roughly and therefore, reliability is not sufficient. Another problem is that when the RFV value exceeds a specified value, clear determination cannot be made whether the problem is limited to the sampled product or related to the entire quantity, and repeated sampling is required.
Third, since the operator takes a sample at appropriate quantity intervals, transfers it, attaches it to the uniformity checking machine, and tests it in succession, the operator cannot help relying on manual work and bears a heavy work load.
This invention provides a snug fitting process apparatus for a tire assembly having a disk wheel and a tire fitted thereto, characterized by comprising;
a rotary drive device for rotary-driving the tire assembly supported on a work holding section,
a first pressing member for performing a snug fitting process by pressing the ground contact surface of the tire assembly,
a second pressing member for coming into pressing contact with the ground contact surface of the tire assembly to receive the radial reactional force of the ground contact surface,
a transfer device for transferring each of the first and second pressing members between a pressing contact position where the pressing member is in pressing contact with the ground contact surface of the tire assembly and a position where the pressing member is released from the pressing contact,
a pressure detecting means for detecting the reactional force received with the second pressing member in the state of pressing contact, and
a process control means for performing in succession; the process of snug fitting by moving the first pressing member with the transfer device and pressing the first pressing member against the ground contact surface of the tire assembly being rotated with the rotary drive device, and the process of measuring the variation in the reactional force with the pressure detecting means by moving the second pressing member with the transfer device and pressing the second pressing member against the ground contact surface of the tire assembly being rotated with the rotary drive device; and performing an RFV judgment based on the reactional force. Using the above constitution, the tire assembly is supported with the work holding section and rotated. The rotary drive device is constituted for example to hold the tire assembly for free rotation with the work holding section and a drive roller is brought into pressing contact with the ground contact surface to transmit rotary force to the ground contact surface. Next, as a snug fitting process, the transfer device presses the first pressing member against the road contact surface of the tire by means of the transfer device. Next, when the snug fitting process is finished, the second pressing member is brought into pressing contact with the ground contact surface and the measurement process is performed. Here, the first pressing member may serve also as the second pressing member. In that case, the first pressing member itself comes into contact with the ground contact surface of the tire assembly to receive the radial reactional force of the ground contact surface. And in the case variation in the reactional force (RFV) is great, it is determined that the snug fitting process is insufficient or the tire or the wheel is not normal.
Here, a proposal is made wherein the transfer device comprises a lock device for making the transfer table immovable, and the process control means comprises a measurement process of pressing and holding the pressing member until a preset reactional force value is detected and, upon detection, making the transfer table immovable, and rotating the tire assembly by operating the rotary drive device to detect with the pressure detecting means the variation in the reactional force.
The above constitution is that the second pressing member is made immovable and pressed against the ground contact surface of the tire assembly. However, it is also possible to constitute that a displacement detecting means is provided to detect the displacement of the tire pressing section, to perform in succession the snug fitting process of transferring with the transfer device the first pressing member and pressing it against the ground contact surface of the tire assembly being rotated with the rotary drive device and the measurement process of pressing the second pressing member with a pressing force made constant with the pressure detecting means against the ground contact surface of the tire assembly and of detecting with the displacement detecting means the displacement of the second pressing member, and to perform the RFV judgment based on the displacement. That is, to maintain the pressing force against the tire constant, it is arranged that the tire pressing section is controlled to move back and forth, and the RFV judgment is performed by measuring the back and forth movement using the displacement detecting means.
A means for judging the uniformity of the tire assembly is proposed wherein the RFV judgment is performed with a peak-to-bottom peak value of the displacement with the pressure acting on the tire made constant. Also proposed is an arrangement wherein the RFV judgment is performed by subjecting to an FFT process the displacement measured with a constant pressure on the tire assembly and by comprehensively considering the n-th component. Further is proposed an arrangement wherein the RFV judgment is performed with a true circular accuracy of a virtual tire shape obtained from the displacement data measured with a constant pressure on the tire assembly. The RFV judgment of the tire assembly with a higher reliability is made possible by using these judgment means singularly or in combination.
It may be arranged that in case the RFV judgment with the process control means results in a reject, the snug fitting process is performed again. In this way, in many cases the variation in the reactional force is reduced and the abnormal state is corrected. The tire assembly subjected to the snug fitting process for the second time is further measured in the measurement process and, if it proves that the RFV has not been corrected, the tire assembly is removed from the production line.
As the first pressing member, a set of plural rollers disposed side by side close to each other and supported for free rotation with a support piece is suitable for use to apply a lateral force to the ground contact surface of the tire assembly by pressing the set of rollers against the ground contact surface of the tire assembly. With this constitution, because of the presence of the slip angle, a lateral force is applied to the ground contact surface of the tire assembly. As a result, the tire and rim are made to fit each other tightly into a favorable state. With the above constitution, since the set of pressing rollers is constituted with the plurality of rollers arranged side by side close to each other, a wide pressing area is formed which is similar to the ground surface on which the actual vehicle runs, and the similar load to that in actual situation acts on the ground contact surface of the tire assembly. Furthermore, since gaps are present among the rollers, the pressing area becomes irregular to some extent and is very similar to the irregular road surface, and similar loads occurring when an actual vehicle runs act on the tire assembly.
Here, a single pressing member may serve as both of the first and second pressing members. In this case, since a single pressing member suffices both of the purposes, the device can be simplified and the cost can be reduced.
The above transfer device may be constituted that; a transfer table to which a pressing member is attached, a feed screw shaft driven for rotation with a servomotor is made to engage with the transfer table, and the transfer table may be stopped at any intended position by controlling the rotation of the servomotor. With this arrangement, the pressing member may be transferred to a position where an optimum pressure is applied to the ground contact surface. When a single pressing member serves as both of the first and second pressing members, the pressing force in the snug fitting process is different from the press-contact force in the measurement process. However, both of the pressures may be easily set with the rotary control of the servomotor.
The above detection means may be arranged that; the tire pressing section is supported to be movable in the direction parallel to movement direction of the transfer table on the transfer table moved in the tire pressing direction with the transfer device, the pressing member is fixed to the tire pressing section, a load cell is held with a radial force between the transfer table and the tire pressing section, and the reactional force of the pressing section relative to the transfer table is detected with the load cell. By reading the pressure detected with the load cell, the RFV may be easily judged.
An arrangement is also proposed wherein the pressure detecting means comprises; a tire pressing section to which is attached a pressing member to be moved in the tire pressing direction with a transfer device, a press-in section which moves along the movement direction of the tire pressing section in the state of being capable of moving to and from the tire pressing section within a specified distance and is driven with a drive means to press the tire pressing section, and a load cell interposed between the tire pressing section and the press-in section; and the reactional force of the tire pressing section relative to the press-in section is detected with the load cell. Here, when the press-in section is transferred in the tire pressing direction with a drive means such as a servomotor or a servo-cylinder, the tire pressing section is pressed with the press-in section and the pressing member attached to the press-in section comes into pressing contact with the ground contact surface of the tire assembly. As the reactional force of the tire pressing section relative to the press-in section is detected with the load cell, the RFV can be easily judged by reading the detected value of the pressure.
With this constitution, it is arranged that a tire pressing section to which is attached a pressing member, and a press-in section are attached to a single sliding mechanism guided in the tire pressing direction and made to be slidable in the tire pressing direction in the state of being capable of moving to and from each other within a specified distance, and a load cell is interposed between the tire pressing section and the press-in section. With this constitution, since a single sliding mechanism guides and moves the tire pressing section and the press-in section, the constitution is simplified.
Here, it is possible to constitute with a means for storing a pressing pattern for the tire snug fitting process to perform the snug fitting process according to the stored pressing pattern. With this constitution, it is possible to bring about appropriate snug fit between wheel and tire quickly by giving varying loads to the tire assembly according to the pressing pattern stored in advance in the control device.
This pressing pattern may be made to correspond to varying loads occurring when an actual vehicle is run or to loads that vary like a sine curve. When the varying loads are exerted to the tire assembly according to the pressing pattern data, snug fit between wheel and tire is realized quickly according to the pressing pattern similar to that occurring during actual run of a vehicle.
Further, a tire assembly manufacturing method is proposed, which method employs the snug fitting process characterized by performing in succession a snug fitting process of pressing a pressing member against the ground contact surface of a tire assembly being rotated with a rotary drive device, and a tire assembly snug fit measurement process of pressing the same or another pressing member against the road contact surface of the tire assembly also being rotated and measuring with the pressure detecting means the variation in the reactional force of the tire. With this manufacturing method, since whether the snug fitting process is appropriately performed is constantly verified in the measurement process and so tire assemblies of stabilized characteristic can be provided. That is, as shown in FIG. 25, in the conventional process, a tire assembly is made in a series of steps; tire and wheel are fitted together, inflated with air, and subjected to a snug fitting process and to a balance correction process, and the snug fit is checked by sampling inspection. In the manufacturing method of this invention, as shown in FIG. 24, the measurement-judgment process can be made immediately after the snug fitting process, the snug fit state is assured for all the tire assemblies, and so the tire assemblies of good quality are provided through such a series of processes.